1. Field of the Invention
The invention relates to a device for automatically detecting various characteristics of an ophthalmic lens, in particular for recognizing the type of lens (constant power or progressive power, for example monofocal, multifocal or progressive lenses), measuring its power, its astigmatism, its prism, and possibly its power in different areas, and then identifying the note-worthy characteristics of the ophthalmic lens concerned, such as, for example, the positions of the optical center and the axis of the cylinder, in the case of a non-progressive lens, or the position of a characteristic point called the “prism reference point” or the axis called the “horizontal axis”, in the case of a progressive lens.
The invention also applies to fitting a centering and drive peg which is glued to the ophthalmic lens for positioning the lens correctly in a grinding machine for imparting to it the required contour, adapted to the shape of the chosen frame.
The invention finds a particularly advantageous application when the device is associated with a lens trimming machine designed to take up a lens after identification of its main characteristics and move it automatically to a grinding station where its contour is modified to adapt it to a chosen frame shape, taking also into account data specific to the user, such as the interpupillary distance and the height, as measured on the wearer.
2. Description of the Prior Art
Trimming an ophthalmic lens, typically by grinding it, necessitates a knowledge of several characteristics specific to the lens. For example, to correct astigmatism effectively using a non-progressive lens, it is necessary to know the position of the optical center and the axis of the cylinder. Indeed, in the case of a non-progressive ophthalmic lens, the optical center must correspond, once the lens is fitted to the frame, to the position of the pupil of the eye. Any offset leads to a prism effect that increases as the power of the ophthalmic lens increases. To correct astigmatism effectively, the axis of the cylinder must also correspond to the axis of the prescribed cylinder. In the case of non-progressive lenses, a device called a lensometer is used to determine these two characteristics manually. The operator moves the lens to locate the optical center and the axis of the cylinder at the same time, and a mechanical device marks the ophthalmic lens at three points that constitute reference points for positioning the lens. The three reference points are then used to center the lens manually on a centering device. The lens is then fitted with a centering and drive peg for locating it in the trimming machine.
In the case of a progressive lens, it is necessary to identify other characteristics, such as the position of a point called the prism reference point (PRP) or an axis called the horizontal axis. A knowledge of these latter characteristics is indispensable for proper correction of the vision of the wearer.
The centering point of the progressive lens, which is the point at which the pupil must be centered, is at a known distance from the PRP, and is therefore known if the PRP is known. Moreover, the horizontal axis gives the orientation with which the lens must be mounted on the frame for proper correction. Progressive lenses always include two relief or diffusing etched markings. These are difficult to see, so lenses often have printed marks that are erased after fitting. These etched or printed markings are used to center the lens, as the lensometer cannot be used to center this type of lens. The segment defined by the two etched markings defines the horizontal axis and the middle of the segment defines the PRP. If the lens is marked, the horizontal axis and the PRP are defined by the marks. A spot defines the PRP and two lines define the horizontal axis. If the lens is not marked, the operator applies marks on top of the etched markings, to make them more visible.
Finally, other types of ophthalmic lens necessitate specific centering operations. In the particular case of lenses known as double-focus lenses, centering is effected using the segment of the lens.
All these centering operations generally terminate in the manual fitting to the lens of a centering and drive peg by means of which the lens is subsequently located correctly in the trimming machine.
To summarize, to be able to center all types of ophthalmic lens known to the person skilled in the art, it is generally necessary to use two devices (a centering device and a lensometer). These operations are usually carried out manually and lead to the fitting of a peg, which operation is also usually carried out manually and constitutes a source of inaccuracies.